1. Field of the Invention
The present invention relates to voltage-controlled oscillators and electronic devices including the same. More specifically, the present invention relates to a voltage-controlled oscillator provided in a cellular phone that utilizes a plurality of communication methods, and to an electronic device including the same.
2. Description of the Related Art
In a communication system, such as a cellular phone system, each communication method and each communication carrier usually occupies different frequency bands. In order for the communication system to operate in different frequency bands, a voltage-controlled oscillator defining a local oscillator for the communication device must operate in a plurality of frequency bands such that the intermediate frequencies are the same.
The following methods have been provided to make the voltage-controlled oscillator usable for a plurality of frequency bands.
(1) Providing a plurality of voltage-controlled oscillators, each having a different oscillation frequency, and the voltage-controlled oscillators are switched for each frequency band.
(2) Integrating a switching element, such as a diode or a transistor, in a resonance circuit of one voltage-controlled oscillator and the resonance frequency of the resonance circuit is switched by turning on/off the switching element.
In method (1), however, the cost increases because a plurality of voltage-controlled oscillators is provided and the miniaturization of communication devices cannot be achieved because a large circuit board is required.
Also, in method (2), problems arise in that providing the switching element increases in the number of components and the cost, and that the size of the circuit board must be increased. Further, the series resistance of the switching element reduces the Q factor of the resonance circuit, thereby deteriorating the C/N characteristic of the oscillation signal. In addition, current must be applied to the switching element, which results in an increase in power consumption.
In order to overcome the above-described problems, preferred embodiments of the present invention provide a voltage-controlled oscillator which operates in a plurality of frequency bands and which reduces the cost of the oscillator, decreases the size of a circuit board, prevents deterioration in the Q factor of the resonance circuit, and decreases power consumption, and also provide an electronic device including such a novel voltage controlled oscillator.
The voltage-controlled oscillator according to a preferred embodiment of the present invention includes an active oscillation element, a resonance circuit connected to the active oscillation element, a varactor diode defining a capacitance element coupled to the resonance circuit, whereby the oscillation frequency of the voltage-controlled oscillator is changed substantially continuously by substantially continuously changing a DC control voltage applied to one end of the varactor diode. The voltage-controlled oscillator further includes a variable DC voltage source that stepwise changes a voltage value. The output of the variable DC voltage source is applied to the other end of the varactor diode.
The voltage-controlled oscillator preferably further includes a voltage divider including at least two resistors connected in series, one end of the voltage divider being connected to the variable DC voltage source and the other end being connected to a reference voltage source. The voltage-division junction or node of the voltage divider is connected to the other end of the varactor diode.
Preferably, the voltage-division junction of the voltage divider is connected to the anode of the varactor diode.
An electronic device according to another preferred embodiment the present invention includes the above-described voltage-controlled oscillator.
With this arrangement, the voltage-controlled oscillator according to preferred embodiments of the present invention is used for a plurality of frequency bands while decreasing the cost and size of the oscillator. Further, a reduction in the Q factor of the resonance circuit and an increase in power consumption of the oscillator are prevented.
Further, in the electronic device according to preferred embodiments of the present invention, cost reduction and miniaturization are achieved.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments with reference to the drawings thereof.